I won't tell him, I promise.

I have been learning from others that the power of names is what we give them. Yes, 'Pest' sounds bad. But it all comes down to whether you like it or not. One day, I will try to talk to your trainer and hear his side of things. If you don't like the name, maybe I can try to convince him to change it. But if you like it, you can keep it. It's up to you, and what makes you happy.